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Scouting for Corn Mould

by 5m Editor
13 November 2008, at 12:00am

A useful guide to identifying common moulds in corn and the mycotoxins associated with each one by Albert Tenuta, pathologist for field crops and program lead at the Ontario Ministry of Agriculture, Food and Rural Affairs.

There are various ear moulds that occur in Ontario and identification is critical since many of these fungi produce mycotoxins, which can have detrimental consequences if fed to livestock, and in some cases humans (ingested or airborne exposure). The persistent wet weather in some parts of the province this summer in conjunction with other factors such as leaf diseases, insect injury (European corn borer, western bean cutworm and others), bird damage, poor pollination etc. could provide the various corn ear rot fungi with the favourable growing conditions necessary for disease development. It is rare in Ontario not to have some hot spots each year and it is in your best interest to be proactive rather then to be caught off guard.

For these reasons, it is important pork producers, and for that matter all corn producers, are able to properly identify the various ear moulds since not all of these fungi produce toxins. Whether your risk is high or not, a pre-harvest assessment for ear moulds and their corresponding mycotoxins is imperative since determining the extent of the ear mould problem prior to harvest is critical to managing and minimizing the impact of these diseases through timely harvest and proper drying/storage conditions.

Determining the levels of deoxynivalenol (vomitoxin or DON) is also important to swine and other livestock producers since DON can have detrimental affects such as poor weight gain and feed refusal. These pre-harvest assessments should be done each year since they can alert you of potential problems and provides time to segregate, obtain alternative corn grain or hold onto stored corn from last year.


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"It is important pork producers, and for that matter all corn producers, are able to properly identify the various ear moulds since not all of these fungi produce toxins."
Check all your fields carefully and note their current condition. A quick method includes scouting 100 plants from the field (5 areas of 20 ears each). Fields with 10% of ears having significant mould growth (20% or more) should be harvested sooner rather then later. Fields with significant mould should have a representative sample collected and tested for toxins, especially deoxynivalenol (DON) prior to storage and feeding. If necessary feed to less sensitive livestock species such as beef cattle or poultry.

Take a Representative Corn Sample

The importance of collecting a representative sample cannot be emphasized enough, since as much as 90% of the variability associated with mycotoxin test results comes from incorrect sample collection. The accuracy of a mycotoxin test is dependent often on a little elbow grease and some inconvenience. Although taking a sample from the top of a storage bin, truck or combine may be easy and very convenient, you will most likely not be happy with the results since mycotoxin distribution is rarely distributed evenly in a load of corn.

If sampling a bin, truck, V-box or other stationary load of corn, a sample probe is recommended. Although ten probes are recommended, five probes will do if necessary.

Mix the grouped sample and take a representative sample from this pooled sample. If you are dealing with a moving stream of grain, either use a diverter or randomly collect cupfuls (handfuls will work as well) of grain.

Regardless of how the sample is taken, it must be processed quickly. Therefore, ship or deliver the sample promptly. The longer the sample sits around, the greater potential of an inaccurate results.

The production of toxins is a major concern when these ear rots are present but it is not always the case that mould growth equates to high toxin samples and vice versa: high toxin levels can occur with little visible fungal growth or ear rot. Either way, it is imperative to access a field and determine which ear moulds and mycotoxins are present. This will allow for the implementation of grain harvest, storage and feeding management options to minimize toxin development or maintain grain quality.

Livestock producers should concentrate on fields with the highest quality and focus on harvest/drying those first in a timely manner and if storing new crop dry corn to under 18% moisture as quickly as possible. This will help maintain quality, reduce fungal growth and limit further increases in mycotoxin levels since both DON and zearalenone production will stop.

Knowing Your Ear Moulds

Gibberella ear rot

The most common and important ear mould in Ontario is Gibberella zeae which is the sexual reproductive stage of Fusarium graminearium. This fungus not only infects corn but also small grains such as wheat and can survive on soybean roots. Gibberella in most cases begins at the ear tip and works it way down the ear plus the husks from infected ears are often tightly adhered to the ear. Although the fungus can produce a white-coloured mould which makes it difficult to tell apart from Fusarium Kernel Rot, the two can be distinguished easily when Gibberella produces its characteristic red or pink colour mould.

Fusarium kernel rot

Unlike Gibberella, Fusarium-infected kernels are often scattered around the cob amongst healthy looking kernels or on kernels that have been damaged for example by corn borer or bird feeding. Fusarium infection produces a white to pink or salmon-coloured mould. A 'white streaking' or 'star-bursting' can be seen on the infected kernel surface. Although many Fusarium species may be responsible for these symptoms, the primary species we are concerned about in Ontario is Fusarium verticillioides (formerly known as Fusarium moniliforme).

Diplodia ear rot

The characteristic ear symptom of Diplodia maydis infection is a white mould that begins at the base of the ear and will eventually cover and rot the entire ear. Mould growth can also occur on the outer husk which has small black bumps (pycnidia) embedded in the mould. These reproductive structures are where new spores are produced.

Penicillium ear rot

Penicillium rot (Penicillium oxalicum) produces a light blue-green powdery mould which grows between the kernels and cob/husk surface. Infected kernels could become bleached or streaked. It can be a serious problem if corn is stored at high moisture levels (greater 18%).

Table 1. Common ear rots and moulds that occur in Ontario and the primary mycotoxins they produce
Corn Ear Rot Description Primary Mycotoxins
Gibberella
(Gibberella zeae, also called Fusarium graminearum (asexual stage))
Red/pink mould.
Begins on ear tip.
Bird, insect injury increases damage.
Deoxynivalenol (Vomitoxin or DON).
Zearalenone (ZEN).
T-2 toxin
Fusarium
(Fusarium verticillioides)
White, pink or salmon-coloured.
Can occur anywhere on ear.
Often begins at the sites of insect damage.
Fumonisins
Diplodia
(Stenocarpella maydis)
White mould.
Begins at base of ear but often entire ear covered.
Black pycnidia (bumps) on husks and kernels
None
Penicillium
(Penicillium oxalicum)
Blue-green mould.
Mould between kernels and on cobs/husk.
Ochratoxins are produced by other Penicillium species.
P.oxalicum does not produce ochratoxin; not detected in Ontario


October 2008